diff --git a/lib/cancan/rule.rb b/lib/cancan/rule.rb
index 82758ba..f86296f 100644
--- a/lib/cancan/rule.rb
+++ b/lib/cancan/rule.rb
@@ -55,7 +55,8 @@ module CanCan
     end
 
     def unmergeable?
-      @conditions.respond_to?(:keys) && (! @conditions.keys.first.kind_of? Symbol)
+      @conditions.respond_to?(:keys) && @conditions.present? &&
+        (!@conditions.keys.first.kind_of? Symbol)
     end
 
     def associations_hash(conditions = @conditions)
diff --git a/spec/cancan/model_adapters/active_record_adapter_spec.rb b/spec/cancan/model_adapters/active_record_adapter_spec.rb
index 2f1b7af..a2c2809 100644
--- a/spec/cancan/model_adapters/active_record_adapter_spec.rb
+++ b/spec/cancan/model_adapters/active_record_adapter_spec.rb
@@ -20,10 +20,12 @@ if ENV["MODEL_ADAPTER"].nil? || ENV["MODEL_ADAPTER"] == "active_record"
         t.boolean "secret"
         t.integer "priority"
         t.integer "category_id"
+        t.integer "user_id"
       end
       model do
         belongs_to :category
         has_many :comments
+        belongs_to :user
       end
     end
 
@@ -37,6 +39,15 @@ if ENV["MODEL_ADAPTER"].nil? || ENV["MODEL_ADAPTER"] == "active_record"
       end
     end
 
+    with_model :user do
+      table do |t|
+
+      end
+      model do
+        has_many :articles
+      end
+    end
+
     before(:each) do
       Article.delete_all
       Comment.delete_all
@@ -233,6 +244,15 @@ if ENV["MODEL_ADAPTER"].nil? || ENV["MODEL_ADAPTER"] == "active_record"
       @ability.model_adapter(Article, :read).joins.should == [{:project=>[:comments]}]
     end
 
+    it "should merge :all conditions with other conditions" do
+      user = User.create!
+      article = Article.create!(:user => user)
+      ability = Ability.new(user)
+      ability.can :manage, :all
+      ability.can :manage, Article, :user_id => user.id
+      Article.accessible_by(ability).should == [article]
+    end
+
     it "should restrict articles given a MetaWhere condition" do
       @ability.can :read, Article, :priority.lt => 2
       article1 = Article.create!(:priority => 1)
diff --git a/spec/cancan/rule_spec.rb b/spec/cancan/rule_spec.rb
index 0fba0ed..9c612cb 100644
--- a/spec/cancan/rule_spec.rb
+++ b/spec/cancan/rule_spec.rb
@@ -44,4 +44,9 @@ describe CanCan::Rule do
 
     @rule.should be_unmergeable
   end
+
+  it "should be mergeable if conditions is an empty hash" do
+    @conditions = {}
+    @rule.should_not be_unmergeable
+  end
 end